1. Field of the Invention
The present invention relates to a cleaning composition for use in processing/molding machines for thermoplastic resins.
2. Description of the Related Art
In the processing/molding fields of plastics, there is the tendency of produce many kinds to plastics in a small amount of each kind, and so the production of the plastics must often be changed from one kind of plastics to another kind. Therefore, it is important from the viewpoint of quality control to clean the interior of a molding machine at the time of the change-over of the plastic.
In the processing/molding step of the plastics, some measures are taken to eliminate the influence of the preceding resin at the time of its production changeover. In particular, when the preceding resin is a colored resin, for example, when the preceding grade having a deep color, such as blue or black is changed to another grade having a light color, such as white, it is required to clean the interior of the molding machine with a cleaning resin, to perform troublesome operations such as the disassembly and cleaning of the processing/molding machine, and to stop the production. For example, in the case of the changeover of the colored product in an extrusion granulation step, an extruder is stopped and a screw is then drawn therefrom, and the screw and the interior of a cylinder are cleaned by brushing or the like, and afterward, the screw must be mounted again. In a manner in which the preceding kind of resin is replaced with a substitution resin without drawing the screw, a large amount of the resin is needed for the cleaning, and soils on intricate structure parts in the extruder cannot be removed. In consequence, there is the problem that the subsequent resin is colored inconveniently. In order to solve these problems, cleaning compounds are used. The employment of the cleaning compound facilitates the removal of the remaining material in the extruder and thereby permits the completion of the grade changeover by the use of a small amount of the substitution resin. The cleaning compounds can be classified into cleaning compounds containing a lubricant such as stearic acid and cleaning compounds containing an acrylic resin having hardness. However, the former is poor in cleaning effect. The latter gives off a strong odor, and since it is used in a semi-molten state, the load increases and therefore the cleaning compound must be used after the disassembly of a die, a breaker plate, a wire net and the like, which means that the problem of a complex operation remains unsolved.
For example, Japanese Patent Application Laid-open No. 62-195045 discloses a composition comprising a thermoplastic resin, a sodium alkylbenzenesulfonate and a water-repellent compound, and Japanese Patent Application Laid-open No. 63-66245 discloses a cleaning composition comprising a thermoplastic resin, a sulfonic acid neutral salt and a powdery inorganic compound having a particle diameter of 0.05 to 10 .mu.m. Furthermore, a combination of these techniques is described in U.S. Pat. No. 4,838,945. In addition, U.S. Pat. No. 4,838,948 discloses a cleaning process for a resin processing apparatus by the use of polyethylene, calcium carbonate and a sulfonic acid salt activator.
However, these techniques are suitable for the so-called general-purpose plastics where a molding temperature is about 300.degree. C. or less. In recent years, engineering plastics and superengineering plastics have come out, and in most of these cases, the molding temperatures are 300.degree. C. or more and in extreme cases, they are in excess of 400.degree. C. This temperature range is noticeably different from that of the general-purpose plastics.
At such high temperatures, the conventional cleaning compounds cannot maintain viscoelasticity at the time of melting, so that the viscosity deteriorates. For this reason, the conventional cleaning compounds are not usable at the high temperatures.
As discussed above, there has not heretofore been any cleaning composition for the color changeover and material changeover of the super-engineering plastics in the molding step thereof. Hence, in the molding of the super-engineering plastics, the removal of the plastics is carried out by using a polycarbonate resin (containing a glass fiber) at about 300.degree. C. to which the molding temperature is gradually lowered from 400.degree. C. Therefore, a part of the resin is lost and the screw in the molding machine tends to be damaged by the glass fibers. Furthermore, it is necessary to raise the temperature of the super-engineering plastics up to the molding temperature again in the subsequent molding step, which requires the complex operation of raising and lowering the temperature and which takes a long period of time. In addition, the cleaning effect is also poor.
Thus, a cleaning composition is desired which can sufficiently maintain viscoelasticity at the melting time even at a high temperature such as 400.degree. C., i.e., the molding temperature of Empla or Super-empla and which can exert the cleaning effect.